Microlithographic projection exposure apparatus often include illumination optics for producing an intensity distribution in an exit pupil associated with object field points in an object field which is illuminated by illumination optics. Such apparatus are known, for example, from U.S. Pat. No. 6,285,443 B1. The structuring (i.e. producing a desired intensity distribution) of exit pupils results from structuring an intensity distribution in angle space, which is produced by a diffractive optical element (DOE) in a plane which is Fourier related by Fourier optics to a subsequent pupil plane. In the exit pupil the intensity distribution is described as a function of pupil coordinates which correspond to angles in the plane of the DOE. Variable zoom objectives and/or axicon systems, which are arranged between the DOE and the pupil plane, may be used to selectively vary the angle distribution produced by the DOE. It is thereby possible, for example, to adjust the coherence of the illumination, for example the outer and/or inner σ of a setting, with σ being the coherence parameter which will be described in more detail below. These adjustable elements make it possible to obtain a more complex structuring of exit pupils. The zoom objective and/or the axicon system can ensure a radially symmetric or axisymmetric redistribution of light about the optical axis of the pupil plane as a symmetry axis. Without restriction of generality, symmetry of the axicon is assumed with respect to the optical axis.
For the coherence parameters indicated above, the outer σ is a measure of the fill factor of light in the exit pupil. Conversely, the inner σ is a measure of the fill factor of central obscuration or shadowing inside the light-filled region in the exit pupil that is described by the outer σ. At least one further set of Fourier optics transforms the distribution as a function of the pupil position in the pupil plane into an angle distribution in a subsequent object plane, so that the exit pupils of the object field points of the object field in the object plane of the illumination optics are structured.
A restricting factor in these projection exposure apparatus can be that structuring produced by a DOE can be modified only to a small extent, essentially radially symmetrically or axisymmetrically with respect to the optical axis, by adjusting lenses of the zoom objective or elements of the axicon system. If a completely different structure of the exit pupil is desired, it is desirable to change the DOE. In practice, the time taken to provide a suitable DOE for the desired pupil structuring may be several days or even weeks. Such projection exposure apparatus are therefore only limitedly suitable for fulfilling the customer's desired rapid change. For example, it is not possible to a change between very different structurings of the exit pupils within fractions of a second.
Projection exposure apparatus for microlithography, having illumination optics for rapidly changing the structuring of exit pupils via multi-mirror arrays (MMA) are known, for example, from WO 2005/026843 A2.
Methods for calculating optimal structurings of exit pupils of illumination optics of a projection exposure apparatus as a function of mask structures to be imaged on the reticle are known, for example, from U.S. Pat. No. 6,563,566 B2 and US 2004/0265707 A1.